Utilizing the same gears which the riders uses to achieve efficiency, mid-drives or crank drives make use of the same gears. The benefits compare to that of hub motors = greater torque, less amperage (significant less motor heat) longer battery life.
New Bafang Crank- Drives
Postby d8veh » Tue May 14, 2013 4:40 am
Bafang were showing two versions of their new crank-drives at the Shanghai show last week. The 250w version is available on Aliexpress as a kit now. I think the "750w" one was more to gauge customer opinion, but I'm sure it'll be available soon. I tried both versions in the area outside the halls, which is totally flat, but I was able to gain some useful info.
Both versions are smooth and quiet. No gearbox noise - just the normal motor noise. The 250w version felt a bit less powerful than a 250w hub-motor, but that might be just an illusion because you get a different feel between the high and low gears.
The 750w version had about the same power as my 350w 36v GeNG Gen 2 with 22 amps, although it was much smoother and quieter. It had a 48v bottle battery, so it was probably running with 15 amps. The two versions looked the same, but they told me that the 750w one was a little wider and had thicker wire. http://www.aliexpress.com/item/8fun-mid ... 97760.html
There were also two other crank-drive motors at the show. One was from Ananda, which was a bit noisier, and another similar one - I forget the name. Both of these required a much larger (ca. 100mm) bottom bracket tube, so OEM only.
It seems to me that the Chinese are not very clever in their development. All the motors had crank-speed sensors on them to detect pedalling. Basically, they had applied their hub-motor technology to a crank motor, but then you get a problem with the motor running on after you stop pedalling, which messes up gear-changing. I reckon some customers had told them that European ones have torque sensors, so one or two had torque sensor versions, but they didn't change the controller software. It feels like they use the torque sensor to switch the power on rather than give a proportional amount. You still get the motor running on. They have to go some way before being able to compete with Bosch, Kalkhoff and Panasonic, but I'm sure that they're working on it. ref: Endless-sphere.com ? View topic - New Bafang Crank-drives
Concerns: As a motor, they're nice - very smooth and quiet, but the problem is the control system. It's adequate, but flawed. Basically, they've used hub--motor technology (sensors and controllers) and applied it to a crank-drive. The worst characteristic is that the motor runs on a bit after you stop pedalling, which keeps tension on the chain. The tension makes gear--changing a bit traumatic, and probably impossible with Shimano hub-gears. I tried one with a Nuvinci hub, and it was a perfect match because you can change gear under load.
Just to clarify, the only motors in production do not have torque sensors. This is why there is a slight delay when you stop pedaling and when the motor stops when using the PAS mode. According to Bafang, they were not satisfied with any torque sensors on the market so they are developing their own for this motor, but it is still 6 months away from production.
This video shows better the custom drive mechanism. The large aluminum sprocket among other components were CNC machined. You will see 2 motors mounted on a frame, the mounting brackets are custom made.
I just got my new Off Road 29er Electric Bike 48V 750W 29er Mid-Drive+9-speed+48V 12Ah Li-ion , this is the bafang 8fun motor... bought it directly from China, very fast delivery...(7 days)... up to 9 PAS modes and 9 gears... this means many combination for the same speed... I would like to have an amp-volt-power indicator to find out what would be the best gear ration to PAS MOde to use... Can I get this information from the original controler??? or do I have to add something to it...